Fluoride Fluorescent Probes Based On Si-O Bond Cleavage

In recent years, the recognition and detection of anions has attracted a wide spread attention because of its important role in many chemical and biological processes. Among the anions, fluoride ion is particularly important. It is a necessary trace element for human body. Low levels of fluoride ion have shown to be effective for prevention of dental caries, treatment of osteoporosis. But high concentration of fluoride intake is harmful to human body, it may cause dental fluorosis, skeletal fluorosis, urolithiasis, and diseases such as cancer. Traditional methods of detecting fluoride are ion chromatography, selective electrode method, fluorine reagent colorimetry and fluorescence probes. Fluorescence anlytical method is highly sensitive and selective, fast and simple. It has low detection limit and strong anti-interference ability.In this paper, we designed and synthesized two highly selective fluoride fluorescence probes based on Si-O bond cleavage, FP and FP-1, for live cells imaging. Probe FP, which based on fluoride triggered Si-O bond cleavage followed by intramolecular cyclization reaction to generate julolidine coumarin derivatives with a high fluorescence quantum yield (φ= 0.84), is highly selective and sensitive for fluoride. FP could be easily prepared as paper test strips to detect fluoride ions in aqueous solutions with a limit as low as 19 ppb. Intriguingly, FP could accumulate preferentially in the mitochondria of living cells, and light up the low concentration fluoride ions (10 μM) in mitochondria with a strong green fluorescence, and without interference from other anions.Probe FP-1, based on cyanostilbene fluorophore, is a two-photon fluorescent probe. It cloud be used for one-photon or two-photon live cells imaging. In DMSO and HEPES (V/V= 7:3) aqueous solution, added fluoride ion, the silicon-oxygen bond repures, and followed by a twisted intramolecular charge transfer (TICT) process, fluorescence of FP-1 quenched, realizing the "turn-off detection for fluoride. FP-1 shows fast response for fluoride with good selectivity and sensitivity. It could be used for live cells one-photon or two-photon fluorescent imaging, detecting the fluoride in cytoplasm, In addition, it is a good bio-imaging molecular switch.